There were two ship radio technicians whose job it was to regularly inspect the buoys. This inspection means opening the bracket door carefully, lifting the beacon to check a signal light comes on (battery check) and then switch the 'off' button before it transmits a distress signal proper. They then record it as checked in the radio logs, which was done a week before the accident. However, whilst this may have not been done but marked off on the log anyway, what Lehtola was referring to here was the reason for it not tuning was in the installation phase [=Asetusvaiheessa] or, as google puts it: 'set-up stage'.
This seems to indicate that the EPIRB's were never properly registered with the satellite via its coding - mandatory for both manual or auto - and thus, when they successfully released from their brackets to the water surface, there was no signal to transmit (some kind of call back). As you know, the EPIRB's were housed on the roof of the bridge's wings, so hard to see how they could be manually switched on even if technically off because of the failure at the installation phase. However, Lehtola was a lawyer so was probably reciting feedback given to him which lacks finer detail. The set-up stage refers not to the inspection and testing phase but to the first installation, which we can see in the word 'Asetus' = set up, to place, to install. This is a different word used from to tune or to arm.